A Navy SEAL was killed and another injured after an accident where they collided in midair during parachute training in southern Arizona on Thursday, according to authorities.

An E-8 senior chief was taken to the University of Arizona Medical Center in Tucson, where he was pronounced dead, said a representative from the Department of Defense.

The second SEAL, an E-6 petty officer first class, was in stable condition at the same hospital, according to military officials.

The names of the SEALs were not released, and are being held for 24 hours after the family of the dead SEAL has been notified, though both are from an East Coast Naval Special Warfare unit, according to Lt. Commander David McKinney, a spokesman for the Naval Special Warfare Command. Military officials said the accident is under investigation.

They were practicing "routine military free-fall training" when the accident occurred around 12:30 p.m. local time Thursday afternoon, said U.S. Special Operations Command spokesman Kenneth McGraw.  He said it was a normal exercise done to maintain readiness. 

The two officers collided in midair and landed in separate areas, authorities said. 

The officers belonged to the same elite unit that included those who participated in the raid on the compound that killed Osama bin Laden two years ago, a source familiar with the situation told CNN.

The command has a parachute testing and training facility at the Pinal Airpark in Marana, according to McGraw. He said the training programs operate there year round. The area is located in a rugged desert terrain that is northeast of Tucson.

This is the second fatal military training accident in the last month and the third since February. A training accident in Nevada killed seven Marines when a mortar exploded inside a tube before launching earlier this month and an additional seven were killed in a helicopter collision.